Manufacture of magnetic heads

ABSTRACT

A method is disclosed in which a pair of electrically nonconducting ferrite pole pieces for use in a magnetic transducing head are assembled together with a non-magnetic separator which defines a transducing gap and in which an electrically conductive film is applied around the pole pieces and the gap. The pole pieces are subsequently encased in non-magnetic material to produce a working face in which the pole pieces and gap are surrounded firstly by the conductive layer and then by the nonmagnetic material. A ferrite block is similarly built up surrounded by a conductive layer and non-magnetic material and the block is then grooved to assume a U-shaped configuration. The assemblies containing the pole pieces and the grooved ferrite block are then brought together so that the U-shaped block forms a yoke for the pole pieces. The block assembly may be further grooved to permit a coil to be introduced over at least one limb of the yoke.

United States Patent [1 1 Case [54] MANUFACTURE OF MAGNETIC HEADS [76] Inventor: Derek Frank Case, 122 Cadbury Rd. Sunbury-on-Thames, England 22 Filed: Dec. 7, 1973 21 Appl. No.: 422,684

[30] Foreign Application Priority Data [58] Field of Search 29/603; 360/122, I24, 125, 360/127, 103

[56] References Cited UNlTED STATES PATENTS 2,800,534 7/1957 Bradford et al.... 360/122 3,195,l19 7/1965 Worosz 29/603 3,384,954 5/1968 Bradford et al.... 29/603 3,601,87l 8/1971 Pierce 29/603 Dec. 30,1975

Primary ExaminerCarl E. Hall Attorney, Agent, or Firm-George R. Douglas, Jr.

[57] ABSTRACT A method is disclosed in which a pair of electrically non-conducting ferrite pole pieces for use in a magnetic transducing head are assembled together with a non-magnetic separator which defines a transducing gap and in which an electrically conductive film is applied around the pole pieces and the gap. The pole pieces are subsequently encased in non-magnetic material to produce a working face in which the pole pieces and gap are surrounded firstly by the conduc tive layer and then by the non-magnetic material. A ferrite block is similarly built up surrounded by a conductive layer and non-magnetic material and the block is then grooved to assume a U-shaped configuration. The assemblies containing the pole pieces and the grooved ferrite block are then brought together so that the U-shaped block forms a yoke for the pole pieces. The block assembly may be further grooved to permit a coil to be introduced over at least one limb of the yoke.

3 Claims, 8 Drawing Figures U.S. Patent Dec. 30, 1975 Sheet 1 of2 3,928,908

FIG .4.

US. Patent Dec. 30, 1975 Sheet 2 of2 3,928,908

MANUFACTURE OF MAGNETIC HEADS BACKGROUND OF THE INVENTION l. Field of the invention The present invention relates to methods of manufacturing magnetic transducing heads.

2. Description of the Prior Art It has previously been proposed to provide eddy current conductors around magnetic transducing heads. Typically the pole pieces of a head are set in a conductive block made, for example, of brass or a conductive head surround is built up from strips or smaller blocks. However, transducing heads have become smaller as the result of improved technology, and it has become increasingly difficult to fabricate the small conductive elements satisfactorily. Moreover, it is desirable that the head surround shall have the same resistance to wear characteristics as the pole pieces themselves and the use of modern ferrite materials makes the matching of wear resistance to the conventional conductive head surrounds even more difficult. The present invention proposes a method of manufacture that permits the use of a conductive surround in conjunction with the insertion of the pole pieces of a head into a working face and avoids the problems associated with the fabrication of a conductive surround from discrete blocks.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of manufacturing a transducing head for use in conjunction with a magnetic recording medium, the head having a working face arranged to be positioned in use adjacent the medium to co-operate therewith and having a pair of electrically non-conductive ferrite mangetic elements forming at the working face magnetic pole pieces separated by a non-magnetic spacer to provide a transducing gap, which method includes forming an electrically conductive layer as a closed loop about an axis substantially perpendicular to said working face, the loop circumscribing only the pole pieces and the spacer at least at and in the vicinity of the working face.

BRIEF DESCRIPTION OF THE DRAWINGS A method of manufacturing a magnetic transducing head assembly embodying the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows a ferrite pole piece element.

FIG. 2 shows the element with a conductive screening layer.

HO. 3 shows a number of screened elements assembled in a non-magnetic support.

FIG. 4 shows a pole piece assembly.

FIG. 5 shows a screened ferrite yoke element.

FIG. 6 shows a number of screened yoke elements assembled in non-magnetic support.

FIG. 7 shows a yoke assembly.

FIG. 8 shows a multi head assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

Referring to the drawings, a pole piece element l shown in FIG. 1 consists of two ferrite strips 2, 3 secured together with a non-magnetic gap 4 therebetween. The element I may be produced by spacing two ferrite bars apart and introducing into the gap therebethickness to correspond to a required track width on a recording medium with which the finished magnetic head is subsequently to be associated.

The pole piece element 1 is then plated with copper 5, FIG. 2, initially by an electroless process and then by an electrolytic plating process to build up a layer of copper of the required thickness.

A mulit track pole piece block is then assembled as shown in FIG. 3, which shows a block from which pole piece assemblies for read and write heads for two tracks may be produced. The plated pole piece elements 1 are positioned in grooves in non-magnatic blocks 6, 7 so that the elements I are spaced apart by the desired intertraek spacing. The blocks 6, 7 are then secured together with a suitable spacer sandwiched therebetween. The spacer consists of a pair of nonmagnetic plates 8, 9 and a magnetic plate 10 sandwiched between the plates 8, 9. The pole piece elements 1 in the block 6 will subsequently be formed into poles of pairs of read heads and the poles piece elements 1 in the block 7 will subsequently be formed into poles of corresponding pairs of write heads, The blocks 6, 7 may be formed of glass-ceramic material and the assembly is secured together by glass or a suitable synthetic resin adhesive.

The assembly consisting of the screened elements I, block 6, 7 spacer 8, 9, 10 is then divided as shown in FIG. 3 along spaced parallel planes to produce a plurality of slices ll. Each slice 11 contains a portion of the length of each element 1 positioned in the required relative relationship by a similar portion of the length of the blocks 6, 7 and the spacer 8, 9, 10 as shown in more detail in FIG. 4. One face 12 of the slice 11 is lapped and polished to a flat surface and the other face 13 is machined to a desired profile to act as a working face and which-will cause a recording medium such as a magnetic tape to contact the exposed ends of each pole piece I in the vicinity of its non-magnetic gap 4. The elements 1 are machined from the face 12 so to remove parts of both pole pieces on each side of the gap 4 to reduce the depth through the thickness of the slice.

A yoke assembly for the above described pole piece assembly may be formed .in a similar manner. Ferrite elements 14 (FIG. 5) having a cross section indentical to that of the elements 1 but without a non-magnetic gap, are plated with copper to provide a layer of copper 28 of required thickness extending around each element l4 and are positioned as shown in FIG. 6 in nonmagnetic blocks l5, 16. The blocks l5, l6 are secured together with a spacer therebetween consisting of nonmagnetic plates 17, 18 and a magnetic plate 19. The blocks 15, 16 may be of glass-ceramic material and the components of the yoke assembly are secured together by glass or a suitable synthetic resin adhesive.

The assembly is divided along spaced parallel planes, as shown in FIG. 6, to produce a plurality of slices 20, each slice containing a portion of the length of each ferrite element 14 supported in a similar portion of the blocks l5, l6 and spacers l7, l8, l9. One face 2l of the slices is lapped and polished to produce a flat surface for co-operation with the lapped flat face l2 of the pole piece assembly and in addition is machined to cut grooves extending into the thickness of the slice from the face 21. Two grooves 22 pass respectively each through a pair of ferrite elements 14 lying on the same side of the spacer l7, l8, 19 so as to form each of the ferrite elements 14 into U-shaped yokes, each yoke having two parallel limbs 23. Two further grooves 24 are cut parallel to grooves 22 and four grooves 25 are out perpendicular to the grooves 22, 24. The grooves 24, 25 extend in the blocks l5, 16 adjacent to but outside the U-shaped yokes so as to extend around three sides of one limb 23 of each of the U-shaped yokes and thereby provide together with grooves 22, recesses circumscribing the limb 23 of each yoke, into which recesses prewound coils 26 are place so as to electromagnetically couple with the yoke. If it is desired to place coils on each limb of the yokes, then additional grooves are cut, parallel to grooves 24, so as to form recesses around the other limbs to accomodate the additional coils. The leads 29 of the coil or coils are brought out along the grooves 25.

As shown in FIG. 8 the pole piece assembly of P16. 4 is mounted with its lapped flat face 12 in intimate contact with the lapped face 21 of the yoke assembly 20 that each U shaped yoke 23 bridges the rear ends of the pole pieces 1 and the copper plating on the yokes -23 makes electrical contact with the corresponding copper plating on the pole pieces 1. An electrical earthing connection is made to the copper plating on each yoke 23 by means of a conductive sheet 27 secured in contact with the rear face of the yoke assembly.

It will be appreciated that the above described method of manufacturing a magnetic head assembly provides closed conductive loops surrounding each pair of pole pieces at least at and in the vicinity of the working face 13 which act as eddy current shields effective to reduce the magnitude of magnetic flux link ing with the magnetic cores through the conductive loops. Furthermore the slotting of the ferrite elements 14 by the grooves 22 removes a portion of the copper plating and hence breaks the closed loop in the region of the yoke which is coupled to the coil 26 whilst providing conductive sheet 27 ensures that all the remaining portions of the copper plating are connected to earth.

While in the above described method of manufactur ing a magnetic head assembly, the pole pieces and yokes are plated with copper it will be appreciated that the method may be modified. For example the plating on the yoke elements 14 need not extend completely around the elements and may be provided on one face only. Conductive materials other than copper may be used for plating the pole pieces and yokes. The pole piece elements may be shaped to the required profiles prior to plating and assembling in the nonmagnetic blocks so as to eliminate machining of the rear ends of the pole pieces when in the pole piece assembly if it is desired to produce pole tips of different section from the remainder of the pole pieces. In this case the ferrite elements 1 are machined to the required profile prior to plating with conductive material and the assembly of FIG. 3 is divided along precisely defined planes so that each slice contains the required profiled pole piece elements.

lt will also be realised that where the rear ends of the pole pieces are machined, as described earlier to shape them to a required profile, then this machining may cut away part of the plating. For example suppose it is required to produce a pair of pole tips at the working face 13 of the head the pole tips being supported by spaced apart limbs formed by the lower portions of the pole piece elements 1. It is possible to form the elements 1 into spaced apart limbs by cutting a slot through them along the line of the gap 4 so that the true gap 4 exists only at the upper end of the element 1. Cutting a slot in this way will also cut trrough a part of the surrounding conductive layer. However, it will be seen that, in effect, this form of structure merely extends the limbs of the U-shaped yokes 14 into the pole piece elements. Thus it will be apparent that there will always be a closed loop of conductive material formed by the conductive layer circumscribing those parts of the pole pieces which form the actual pole tips and which are separated by the transducing gap at and in the vicinity of the working face of the head.

If desired the magnetic cores may be formed of other magnetic materials such as mu-metal. For example preformed laminations of mu-metal are bonded together and are then plated at least in the vicinity of the pole tips with a conductive layer to form a closed conductive loop circumscribing the pair of poles and the spacer in the transducing gap.

I claim:

I. A method of manufacturing a transducing head for use in conjunction with a magnetic recording medium. the head having a working face arranged to be positioned in use adjacent the medium to co-operate therewith, the method including the steps of assembling a pair of electrically non-conductive ferrite elements and a non-magnetic spacer so as to provide at the working face magnetic pole pieces separated by the nonmagnetic spacer the latter defining a transducing gap; depositing an electrically conductive layer over the assembled ferrite elements to provide a closed electrically conductive loop about an axis substantially perpendicular to the working face and such as to circumscribe only the pole pieces and the transducing gap at least in the vicinity of the working face, forming a nonmagnetic block grooved to receive the assembled elements; inserting the assembled elements with the conductive layer thereon into the groove with the spacer between the ferrite elements layer parallel to the axis of the groove; applying a plate of non-magnetic material to bridge the groove; and bonding the elements in the block and the plate to form an assembly having a face in which the ferrite elements are separated by the pieces into a required configuration. 

1. A METHOD OF MANUFACTURING A TRANSDUCING HEAD FOR USE IN CONJUNCTION WITH A MAGNETIC RECORDING MEDIUM, THE HEAD HAVING A WORKING FACE ARRANGED TO BE POSITIONED IN USE ADJACENT THE MEDIUM TO CO-OPERATE THEREWITH, THE METHOD INCLUDING THE STEPS OF ASSEMBLING A PAIR OF ELECTRICALLY NON-CONDUCTIVE FERRITE ELEMENTS AND A NON-MAGNETIC SPACER SO AS TO PROVIDE AT THE WORKING FACE MAGNETIC POLE PIECES SEPARATED BY THE NON-MAGNETIC SPACER THE LATTER DEFINING A TRANSDUCING GAP; DEPOSITING AN ELECTRICALLY CONDUCTIVE LAYER OVER THE ASSEMBLED FERRITE ELEMENTS TO PROVIDE A CLOSED ELECTRICALLY CONDUCTIVE LOOP ABOUT AN AXIS SUBSTANTIALLY PERPENDICULAR TO THE WORKING FACE AND SUCH AS TO CIRCUMSCRIBE ONLY THE POLE PIECES AND THE TRANSDUCING GAP AT LEAST IN THE VICINITY OF THE WORKING FACE, FORMING A NON-MAGNETIC BLOCK GROOVED TO RECEIVE THE ASSEMBLED ELEMENTS; INSERTING THE ASSEMBLED ELEMENTS WITH THE CONDUCTIVE LAYER THEREON INTO THE GROOVE WITH THE SPACER BETWEEN THE FERRITE ELEMENTS LAYER PARALLEL TO THE AXIS OF THE GROOVE; APPLYING A PLATE OF NON-MAGNETIC MATERIAL TO BRIDGE THE GROOVE; AND BONDING THE ELEMENTS IN THE BLOCK AND THE PLATE TO FORM AN ASSEMBLY HAVING A FACE IN WHICH THE FERRITE ELEMENTS ARE SEPARATED BY THE TRANSDUCING GAP AND SURROUNDED BY NON-MAGNETIC MATERIAL.
 2. A method of manufacturing a transducing head as claimed in claim 1 further including the step of shaping the face of said assembly to form the working face.
 3. A method of manufacturing a transducing head as claimed in claim 2 further including the step of removing material from that face opposite said working face parallel to and around the spacer to shape the pole pieces into a required configuration. 